Since the features of a fiber-reinforced composite material such as excellent heat resistance or mechanical strength as well as a light weight have been highlighted, the use of a fiber-reinforced composite material for various structures including housings or various members of an automobile or airplane has extended. With respect to a matrix resin of the fiber-reinforced composite material, various performances such as a high impregnation capability into reinforcing fibers, excellent storage stability, and high curing properties without causing voids and excellent heat resistance, mechanical strength, and fracture toughness of a cured product thereof are required. Development of a resin material having an excellent balance between these various performances is required.
As a resin composition having high heat resistance and high toughness, for example, an epoxy resin composition has been disclosed, which contains a trisphenol methane-type epoxy resin in which a ratio of a peak (a), which corresponds to an ortho-orientation skeleton, to a peak (b), which corresponds to a para-orientation skeleton as measured by 13C-NMR, is 0.25 to 0.27 and a curing agent (PTL 1). However, the impregnation capability into a base material of this curable composition tends to deteriorate as the viscosity is increased, and additionally, a sufficient elastic modulus is not obtained in a cured product.
Meanwhile, as a resin composition having excellent heat resistance and moisture resistance, a novolac resin having a trisphenol methane-type skeleton in which a proportion of an ortho-ortho-ortho bond is 70% by mole or more with respect to all the bonds, and a composition including the novolac resin are disclosed (PTL 2). However, this curable composition does not have sufficient heat resistance when produced as a cured product, and accordingly, is not suitable for an application which requires high heat resistance.